Pyrometallurgical copper refining



Aug. 11, 1-931.

H. H. SII'OUT 1,817,935

PYROMETALLURGICAL COPPER REFINING Filed Aug. 15, 1928 2 Sheets-Sheet l IHHH Um w? Aug; 11, 1931. H. H. STOUT PYROMETALLURGICAL COPPER REFINING Filed Aug. 15, 1928 2 Sheets-Sheet 2 BY M Patented Au 11, 1931 UNITED STATES PATENT OFFICE HARRY STOU T, OF CLIFTON, ARIZONA, ASSIGNOR T COPPER DEOXIDATION COR- PORATION, OF NEW YORK, -N. Y., A CORPORATION OF NEW YORK PYROMETALLURGICAL COPPER REFINING Application filed August 15, 1928.

This invention relatesto the pyrometallurgical refining of copper.

This application is in part a continuation .of my prior applications Ser. No. 607,427, filed Dec. 16, 1922, and Ser. No. 111,887, filed May 26, 1926. Y

The object of the invention is to produce at less cost a fire-refined product with chemical and physical properties superior to those of the product of previously known refining methods.

A particular object is to produce a copper having uniform and dependable physical qualities, a result ,which cannot be reached is by prior art fire-refining practice.

In the drawings:

Figure 1 is a diagram representing the location of the different units used in carrying out the invention. 4

Figure 2 is an elevation partly in section of certain pieces of apparatus.

Figure 3 is a section of a line 3--3 ofFigurer 2.

During the oxidizing, poling, and casting periods in the reverberatory furnaces used for present fire refining practice, fuel gases are in contact with the molten metal. Since it is impossible to obtain fuel and burn it in such manner that its gases do not contain partial pressures of the detrimental substances such as sulphur, oxygen, sulphur dioxide, carbon dioxide, hydrogen sulphide, water vapor and hydrocarbons, it follows that it is impossible to produce a product free from them.

The absorption of these impurities by contact with the fuel gases is reduced by using large capacity casting machines and thus shortening the exposure time, but this remedy has physical limitations.

By lowering the temperature, the absorption of impurities is reduced, but if the temperature of the copper is lowered in the furnace below about 117 0 (1., the metal freezes on the ladle lips in pouring.

Another source of contamination of present process fire refined copper is the oxygen absorbed by the molten metal in transit from 3 the interior of the furnace to the mould and Serial No. 299,666.

during the solidification in the mould. My experimentation on this point disclosed:

A. Previous investigators and presentpractice operators believe the amount of oxygen absorbed by the molten copper in transit from the furnace and in the mould is negligible. This conclusion was arrived at by comparing poured sample with product sample. The poured sample itself often absorbs more oxygen than the product due to its diminished pouring rate.

B. I have proved by accurate technique in obtaining a true sample of the copper in the furnace, that the amount of oxygen thus absorbed is very appreciable. Depending on the pouring rate and on the cascade rate, I have found it to vary in the refined copper product (not considering anodes) of present practice fire refining plants approximately Y as follows: expressed in per cent. of metal product,- 0 content in furnace from about 0.032 to 0.022 O absorbed from air 0.008 018 0 content product.. 0.040 0:040

C. Not all of the oxygen thus absorb ed is converted into O.Eubecause the time before solidification is not sufficient; hence part of it remains as C11 0 flakes or crystals.

My experimentation disclosed that in the present fire refining practice a readjustment in the elements and compounds in the molten copper occurs during its transit from the furnace and during the solidification in the mould, as follows:

A. Reduction of Hpartial pressure from fuel gases to atmosphere and cooling of the metal causes liberation of H upon emerging from the furnace which continues until solidification occurs. If solidification is too rapid, H is entrapped producing gas pockets.

B. Increased 0 partial pressure in atmosphere over that in the fuel gases, causes 0 absorption as explained above and equilibrium readjustment begins.

C. As the temperature of the metal from the furnace and in the mould falls, the various substances presei t crystallize out at or below their melt points as illustrated by the following:

First.-Excess C11 0 1210 C. Second-Excess (lu s 1127 C. Third.Excess copper crystals 1083 C. Fourth.-.Eu 1067 C. Fifth.-O.Eu 10tA C.

(S.Eu=copper-cuprous sulphide eutectic) (O.E u=copper-cuprous oxide eutectic) D. As each one of the substancesis withdrawn, by crystallization, readjustment of equilibrium begins. When the excess copper crystallizes at about 1083 (3., it leaves the two eutectics (sulphide and oxide) as liquids separating the copper crystals. During the fall in temperature from about 1083 C. to 1067 (1., the two liquid eutectics react upon each other to readjust the equilibrium as follows:

2 011.0 +ou.s=6 ou+so.

Solidification of these eutectics at 1067 C. and 10649 C. puts an 'end to the readjustment. Part of the S0 thus liberated escapes but part is entrapped and appears as gas pockets in the matrix areas between the dendrites.

My experimentation disclosed that for the same sulphur content in molten copper in the reverberatory furnaces used in present fire refining practice, the relative amounts of O.Eu present influences the per cent. of the total sulphur which enters into SE11 solution and the per cent. which remains as Cu S.

A. Raising the oxygen content of the molten copper in the furnace diminishes the per cent. of the total sulphur content which enters into SE11 solution; hence less S0 gas is generated during solidification and the surface of the bar is flat or concave-low pitch copper.

B. Lowering the oxygen content has the opposite effect and the surface of the bar is slightly convexhigh pitch copper.

C. An exaggerated form of B is known as overpoled or sulphur 'worm copper and this condi ion of excess S.Eu solution having occurred in the molten copper in the presence of the partial S pressure of the fuel gases. it is necessary to completely reoxidize the charge in order to unbalance the S.Eu solution equilibrium and then again pole the metal.

My experimentation as outlined above discloses the fact and the reasons why it is physically impossible to produce by present practice fire refining methods a cast copper product which does not contain certain very detrimental impurities. It follows that the refiner makes a compromise product which the fabricator will accept because he can obtain no better, but which possesses physical characteristics which result in high fabricatingv costs and excessive rejects.

7 pockets vary widely in different parts of the same bar; hence rejection of ductility tests by A. S. T. M.

Summarizing the disclosure of my experimentation on the causes of physical imperfectons of present practice fire refined prod uct. these defects are caused by the presence in the product of Cu O, O.Eu, Cu S, S.Eu, H. These substances are formed from the presence in the copper of the following elements,sulphur, oxygen, hydrogen.

If these three elements can be substantially removed from the copper at suitable points in. the operation and thereafter, until solidification, the metal be not subjected to a partial pressure of these elements, wh ch will cause reabsorpticn, a product free from the physical defects caused by these elements and/or their compounds can be produced. This result can be attained by the' process disclosed hereinafter.

In carrying out the process, molten copper melted by any of the methods now used in the art and/or molten copper from the converter 10 is transported by the ladle 11 and poured through the launder 12 into the oxidizing vessel 13, which has been preheated by any suitable method. The preheating has been carried to such a point that the combined heat of the vessel and that of the entering copper results in a copper temperature of from about 2000 to 2050 F. o The copper is then oxidized by any of the methods now used in the art, such as by air and/or oxygen to about a saturated liquid solution'of copper cuprous oxide eutectic at the particular temperature, thereby removing substantially all of thesulphur with the least addition of oxygen. The degree of oxidation necessary to remove substantially all sulphur is a function of the temperature of the copper at the finish of the blow, the lower the copper temperature, the lower the oxygen content necessary; in practice we have about 0.55% oxygen at 2030 F. The partier-219.1 temperature used at the end of the oxldation is that found most economical unflakes, not in eutectic soder the local conditions of fuel cost, wages, necessary tonnage per vessel, WhlCh 1s claimed per se in my copending application Serial No. 5-i7,013, filed June 26, 1931, for Vessel for fire refining, etc.

The oxidizing vessel is specially heat-insulated (as hereinafter disclosed) to prevent rapid loss of heat from the copper, and in some cases it is preferred to pour the oxidizedcopper without further heating into the reducing vessel 14. But the copper cuprous oxide eutectic may be heated by the combustion of commercial fuel to any desired temperature before it is transferred to 4 the subsequent vessel, if found desirable, as

"2275F., a temperature high enough that after reduction and until casting is cznnplete no application of heat to the copper is necessary. i

After the eutectic is in the reducing vessel and before reduction begins it may be fired on by flame from commercial fuel as the eu ectic as such will not absorb appreciable amounts of sulphur beyond that which is substantially expelled by the hydrogen content of the reduction medium during the early stages of reduction when the oxygen content of the copper is re'atively high.

When heating the empty reducing vessel and/or in heating the eutectic in the reducing vessel by application of commercial fuel flame, it was found that fuel of relatively high sulphur content can be used if the combustion gases have a suitable excess oxygen content.

In this vessel the eutectic is reduced to any desired oxygen content by any of the means new used in the art such as poles, charcoal, suitable reducing gases, etc., and from this vessel the refined copper is cast by any of the means new used in the art which will cast the charge in a suitably short casting period time. For errample, the vessel'l4 may be moved along track 17 and thefcopper poured into molds 18.

The oxidation and reduction can be performed in the same vessel, and the copper cast without subjecting it to contact with lame from combustion of commercial fuel after reduction provided the vessel is suitably heat insulated and the casting period sufficiently short, but in this case the interior rick lining of the vessel will absorb appreciable sulphur from the copper before it is oxidized and this sulphur will reenter the copper from the brick work during the latter stages of reduction, and the productcontains relatively more sulphur than the product when oxidation and reduction are conducted in separate vessels. On the other hand the product, even when oxidation and reduction are performed in the same vessel, contains.

appreciably less sulphur and is of superior quality to the product of prior art practice due to its not being contaminated, during and after reduction, by contactwith the combustion gases of commercial fuel. When oxidation is done in the first vessel there is no appreciable sulphur in the copper cuprous oxide eutectic when it enters the reducing vessel and hence the brick work of the reducin vessel is not contaminated with sulphur, anc the resulting product is substantially sulphur free.

It was found that if after reduction is completed to any desired point no flame is allowed to come in contact with the copper, the hydrogen in solution, from the reducing mediums used, escapes from the copper, without the necessity of degasification, and does not appear as blow holes in the product. If, on the other hand, the flame is in contact with the copper during casting, such hydrogen will not escape from the copper and will appear as blow holes in the product.

It was found that in order to maintain the molten copper in thereducing vessel after reduction and during casting at the required temperature for proper casting operations,

the vessel must be especially insulated against loss of heat and must have its openings necessary to conduct the process, capable of being closed relatively tight against the entrance of air into the vessel during the casting period; otherwise fuel is necessary during the casting period, which, as has been pointed out, poisons the copper when in the reduced condition.

It was found that any heat insulating material used in the construction of the vessels became impregnated with copper due to the molten copper penetrating between the joints in the brick work and as soon as this occurred the heat insulating qualities were materially affected. One remedy for this was to increase the thickness of the brick lining to the point where the penetrating molten gopper solidified before reaching the heat insulating material the thickness of brick which this method required was so great that the vessel became so large as to become economically unworkable.

A practicable solution was reached by con- The lining 20 of refractory brick is of such a thickness that the steel shell 21 never rises above a temperature that it is well able to withstand over, long periods of use. The steel shell extends a safe distance above the molten copper level. The next lining 22 of the vessel is composed of a suitable heatinsulating material such as sil-o-cel, magnesium, asbestos, etc., and this lining must be of suitable thickness to retain most of the heat within the vessel and at the same time permit the steel shell 21 to stay below its suitable working temperature. Outside of this heat-insulating material is the outer metal shell 23. The oxidizing and reduclng,

vessels may both be constructed in this manner.

This construction prevents the penetration of the heat insulating material by the copper and the fuel economy resulting is shown by the fact that prior art furnaces receiving molten blister from a converter and fire refining it in the prior art furnaces requires from 95 to 120 pounds of fueloil per ton of refined cast product in the process, while the vessel disclosed uses from to 19 pounds of fuel oil per ton of refined cast product.

The present process differs from prior art practice also in that prior art requires a much higher capital expenditure per ton of product as the following example will show. To produce 240 tons per day of product, fire refined from molten blister, requires by prior art methods two furnaces of 120 tons each or.2aO tons total, from each furnace one charge in hours is cast and the casting periodis from 3 to 5 hours long for each charge. With my process two vessels each approximately tons or a total vessel size of tons, will cast the same amount of copper, a charge is cast every two hours and the casting period for each charge is from 18 to 26 minutes.

The large size furnace units of the prior art require continuous combustion of fuel and therefore need an oxidizing flame during reduction and casting. They consume from 52 to 83 pounds of poles per ton of product. In the present process no fuel is required during reduction and casting, only from 23 to 32 pounds of poles are used per ton of product, and the length of time required for reduction is correspondingly shorter.

In order to producedeoxidized billets, cake, etc., by the use of soluble deoxidizers, prior art practice necessitates the hand ladling and hand casting of such deoxidized copper and the addition of the soluble deoxidizer in the hand ladle and/or in the hand poured crucible. This is because the combustion'contact of oxidizing combustion gases of commercial fuel during the casting period in prior art furnaces oxidizes the soluble deoxidizer as rapidly as it is added to the molten copper. ln the present process any of the soluble deoxidizers now used in the art, such as phosphorus, silicon, zinc, etc., can be added to the previously substantially deoxidized copper in the furnace and the copper cast in the same manner as any other form of copper, thus eliminating the ver expensive hand ladling and hand casting o deoxidized copper.

The excess amount of such soluble deoxidizers in the deoxidized copper in the furnace is only that which by the casting methods used will fix as an oxide of the soluble deoxidizer all oxygen absorbed by the molten copper in transit from the furnace into the mould and during solidification in the mould.

I claim:

1. The process of fire refining copper which includes chemically reducing previously oxidized molten copper without applyin heat to the copper after the start of the re ucing step.

2. The process of fire refining copper which includes chemically reducing previously oxidized molten copper in a vessel having a basic inner lining without applying heat to the copper after the start of the reducing step.

3. The process of fire refining copper which includes chemically reducing previously oxidized molten copper in a vessel having a basic inner lining and a heat-insulating outer layer without applying heat to the copper after the start of the reducing step.

4. The process of fire refining copper which includes chemically reducing previously oxidized molten copper without applying heat to the copper afterthe oxygen content is reduced below 0.2%.

5. The process of fire re includes chemically reducing previously oxidized molten'copper and casting the copper without applying heat to the copper after the start of the reducing step 6. The process of fire refining copper which includes pouring previously melted molten copper containing sulphur into a vessel and oxidizing it to a saturated solution of copper cuprous oxide eutectic, at a temperature below 2075 F. and above 2000 F., thereafter heating the copper to a'temperature in excess of2150 F. by burning commercial fuel inside the vessel, transferring the molten copper to a second vessel, and chemically reducing the copper in the second vessel.

7. The process of fire refining copper which includes pouring previously melted molten.'

copper containing sulphur into a vessel having an inner refractory basic lining and an outer heat-insulating lining and oxidizing it toasaturated solution of copper cuprous oxide eutectic, at a temperature below 2075 F. and above 2000 F, thereafter heating the copper to a temperature in excess of 2150 F. by

burning commercial fuel inside the vessel,

chemically reducing the copper in the second vessel.-

8. The process of fire refining copper which i includes pouring previously melted molten copper containing sulphur into a vessel and oxidizing it to a saturated solution of cop er cuprous oxide eutectic, at a temperature elow 207 5 F. and above 2000 F., transferringthe molten copper to a second vessel, and

chemically reducing the copper in the second vessel, sufficient additional heat having been supplied to the copper after the oxidizing step to avoid the necessity of adding additional heat during the reducing step.

9. The process of fire refining copper which consists of oxidizing molten copper to approximately a saturated liquid solution of copper cuprous oxide eutectic at approximately 2030 F., transferring the copper to a.

heat-insulated vessel, chemically reducing the 

